Going back years there's been talk and early work on bringing DBus into the Linux kernel and since earlier this year the work has been progressing faster with Greg Kroah-Hartman (and others) working on KDBUS while the user-space support code has been going into systemd. With the latest code as of this week, the newest KDBUS and systemd code can yield a booting Fedora 20 system. This code should work on other modern Linux distributions too but was just tested against F20 given that most of the systemd developers involved are employed by Red Hat.
Lennart Poettering wrote on the systemd mailing list, "We reached a major milestone in kdbus development today. We have all the userspace and compat stuff ready to make a full Fedora system boot cleanly and work fine with kdbus on the backend. With current git kdbus and current git systemd things should just work."
Lennart went on to share many details via a Google+ post. The systemd side of the code is considered "pretty much complete" with the exception of user-space policy enforcement.
One of the benefits of having DBus IPC message bus system in kernel-space is less context sqitches needed compared to the traditional user-space daemon.